Vertebral bodies include 32 to 35 vertebrae constructing a torso and intervertebral discs, and serve as a backbone of a human body that connects to cranial bones at an upper end of the human body to the pelvis at a lower end.
The vertebrae consist of 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, 5 sacra, and 3 to 5 coccyges. For an adult, the 5 sacra fuse to form one sacral bone, and the 3 to 5 coccyges fuse to form one tailbone.
Spinal fusion has long been used as a method to treat severe spinal diseases. For example, some or all intervertebral discs need to be eliminated in a typical disc surgery.
This order is mainly performed on the cervical region and the lumbar region, but may also be performed on the thoracic region.
Cages which have been used for spinal interbody fusion come in various external shapes.
The upper and lower portions of a cage are formed in a shape of sawteeth arranged in a line in order to prevent displacement of the cage inserted into the vertebral body. However, it is not certain that the structure formed in the shape of sawteeth arranged in a line serves to prevent displacement of the cage.
Such conventional cages cannot stay fixed by itself, and thus need to be stably fixed using pedicle screws. Accordingly, it may take a considerable time to perform spinal interbody fusion. In addition, fusion of vertebral bodies may be retarded, or the cages may be displaced.